I. Field of the Invention
The present invention relates to time delay circuits.
II. Description of the Prior Art
Time delay circuits are actually known; for example, West German Patents No. DT-AS 1 902 496 and No. DT-AS 2 321 177. In case of the known timing relays with a time delay circuit of this type, the controlling alternating potential, that is, the supply potential or a similar potential, is rectified and applied to the timing cycle in the form of a substantially filtered direct potential with very small amplitude. The timing cycle is equipped with a programmable unijunction transistor which can be advantageously employed as a controllable semi-conductor element and an RC series circuit. An auxiliary potential is taken from the direct potential by means of a resistive voltage divider and applied to the gate of the programmable unijunction transistor as a reference potential. The potential of the auxiliary potential is the parameter which determines the time cycle. If after the application of the controlling supply alternating potential, the potential which is built up over a period of time, which potential is lower at the condenser of the RC series circuit, exceeds at the anode the potential of the auxiliary potential at the gate of the programmable unijunction transistor, this transistor is brought from its first closed condition into its second conductive condition and, thus, it applies a potential to a relay switch directly or via another switching unit such that this relay switch is turned on or turned off, respectively.
This known circuitry, in general, functions quite satisfactorily; however, for the most simple controlling functions for industrial installations with timing relay, it is too elaborate with regard to its economy and with regard to its technical aspects.
III. Prior Art Statement
The aforementioned prior art, in the opinion of the applicant, constitutes the most relevant prior art of which applicant is aware.